In a computer network environment such as the Internet, entities such as people or companies provide information for public display on web pages or other online documents. The online documents can include information provided by the entities via a computing device for display on the Internet. Content items can also be provided by a third-party content provider for display on the documents together with the information provided by the entities. Thus, a person viewing a document can access the information that is the subject of the document, as well as third-party content items that may or may not be related to the subject matter of the document. In some cases, the content provider may wish to determine the effectiveness of a content item in producing conversions associated with that content item.